1. Field of the Invention
The present invention relates to a twin-screw kneading apparatus which kneads materials to be kneaded such as rubber and plastics.
2. Description of the Related Art
A twin-screw kneading apparatus has generally a configuration of manufacturing continuously a kneaded product through a series of operations comprising the steps of arranging a pair of screw sets including kneading segments provided with kneading blades such as rotor segments or kneading disk segments in a chamber communicating from a side to the other side, charging a material to be kneaded such as rubber or plastics from a charging port on one side, forming a kneaded product of a desired state of kneading through kneading at kneading segments while transferring the charged material by the rotation of the screw sets to the other side, and discharging the kneaded product from a discharge port on the other side to outside.
The foregoing kneading is accomplished by applying a rotation force of the kneading segments as a shearing force to the material to be kneaded. It is known that the shearing force becomes maximum at a gap (tip clearance) between the kneading segment and the inner wall of the chamber, and this maximum shearing force increases according as the tip clearance decreases. Therefore, by reducing the tip clearance, it is evidently possible to promote kneading under the effect of dispersing action of the large shearing force. A smaller tip clearance imparts however a locally high shearing force to the material to be kneaded, resulting in early heating of the material to be kneaded to a high temperature.
When manufacturing a kneaded product having a relatively low allowable temperature such as rubber, therefore, measures are taken to set an increasing tendency of the tip clearance so that heating to a temperature over the allowable level even at a low kneading efficiency. When manufacturing a kneaded product of a high allowable temperature, it is the usual practice to sufficiently reduce the tip clearance so as to obtain a large shearing force, placing importance on the kneading efficiency. The conventional continuous kneading apparatus is, as described above, to accomplish kneading by selecting an appropriate tip clearance in response to the kneading conditions such as the kind of material and viscosity, and rotating the kneading segments with the selected tip clearance.
In the aforesaid conventional configuration, however, the tip clearance is appropriate only for specific kneading conditions. When the kind of the material is changed over, requiring different kneading conditions, for example, it is necessary to replace the kneading segments so as to achieve a tip clearance corresponding to the new kneading conditions. Unless this replacement is properly conducted, the tip clearance would be too large or too small to ensure sufficient kneading or dispersion or heating to a temperature over the allowable temperature may be caused.
The present invention has therefore an object to provide a twin-screw kneading apparatus which permits satisfactory kneading and dispersion of a material to be kneaded under various kneading conditions into a desired state of kneading, and enables to prevent an excessive increase in temperature.